Cable television systems have made possible the transmission of many channels of television programs to the homes of subscribers. Instead of being limited to the number of VHF and UHF channels that can be transmitted and received in a given area, the number of channels in cable systems is limited only by the transmission characteristics of the cable itself and the ability to compress the information in television programs into narrower-bandwidth channels. The advent of fiber-optic transmission systems for use in cable television networks has also vastly increased the number of channels available.
Such increase in channels has also given rise to proposals for interactive television systems wherein a subscriber can transmit information or requests back into the system, which information or requests may subsequently affect programs or information directed to such subscriber. There are a wide variety of applications for interactive television systems, such as video games, video catalog shopping, teaching systems, movies on demand and audio programs. Each application can be tailored for an individual subscriber, for example, a subscriber may be able to select the language of the soundtrack in a movie. However, such systems typically require the ability (i) to control specific programs or information sent to each subscriber and (ii) to receive input messages or requests from the subscriber.
In many cable television systems, a special converter is used at the subscriber location to allow the subscriber to select among the various available channels, and possibly to "unscramble" premium channels for which extra fees are payable. Such converters usually provide an output on one of the channels that a standard television receiver can receive, such as Channel 3. More recently, television receivers and video recorders have been made available that are "cable ready," that is, with the ability to receive and select among all the channels transmitted over the cable system, but without the ability to unscramble premium channels. A convener is still needed for the premium channels.
In order to implement many of the features of interactive television systems, it is necessary for messages containing information or requests from subscribers to be transmitted to a central control location. It is desirable for these "uplink" messages to be transmitted from subscribers over the same facility used to distribute programs. Conventional cable systems use frequencies above 50 MHz, allocated in 6 MHz distribution channels, for programs and frequencies in the 5-30 MHz band for such uplink messages. However, because many subscribers will be sending messages over the same uplink frequencies, some means is needed to coordinate such messages to prevent interference and to identify the source of each message.
When a subscriber is first connected to a cable television system with converters at subscriber locations, it is typically necessary for a service technician to install and initialize a converter for such subscriber in the field. Also, a visit by a technician maybe needed to re-initialize a converter after a service interruption or a power failure. Such visits can be costly. Accordingly, it is desirable to provide a converter that can be initialized remotely over the cable system so that such a converter can be furnished to a subscriber for serf-installation and for remote initialization or re-initialization.